Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: areolate to subsquamulose, 0.2-0.4 mm thick, irregularly spreading to 1-3 centimeters across, with distinct margins, lacking a prothallus areoles: subangular to rounded in outline, flat to convex, 0.5-2 mm wide, partly subdivided by fine cracks, when aggregated in groups separated by broader cracks, flanks pale to black, attached by a central hyphal bunch surface: gray, wrinkled to finely cracked, dull, pruinose or not anatomy: upper cortex: indistinct but composed of 1-2 layers of ±round to angular brown cells 5-8 µm in diam. continuing laterally down the flanks of the areole, overlain by a thin (c. 10 µm),, irregular epinecral layer; algal layer: distributed throughout the thallus but less dense below or concentrated into a distinct zone 100-150 µm thick, with algal cells 8-13(-16) µm in diam.; mycobiont portion: ±paraplectenchymatous, composed of cells 5-8 µm in diam.; alga-free medulla: subparaplectenchymatous, with ±round to angular cells 6-11 µm in diam., with with perpendicular colorless to pale brown filamentous hyphae (4-6 µm thick) congregated to form a thick central stipe fixing the areoles Perithecia: one to several per areole, often in groups of 2-3, usually emerging from the cracks subdividing the areoles and thus in surface view connected by fine cracks, becoming situated at the margins of the areoles by dividing processes, spherical, black, up to 0.4 mm wide, tips ±emergent, convex; exciple: globose, 0.2-0.3 mm wide, pale brown to blackish brown, 25-35 µm thick; involucrellum: completely encircling the exciple, 35-50 µm thick, carbonaceous; periphyses 20-30 µm long, 2-3 µm thick, simple or sparsely anastomosing asci: subcylindrical to oblong-clavate, 60-75 x 13-20 µm, 8-spored ascospores: hyaline, simple, subglobose, 9-12 x 7.5-10 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on different kind of rocks (limestone, granite and sandstone), in upland areas World distribution: scattered in Europe, North Africa, North America, and China Sonoran distribution: Arizona (Coconino County) and California (Riverside Co.). Notes: The combination of the complete involucrellum and very small, subglobose spores is diagnostic of Verrucaria spaerospora. The species as presently understood may be heterogeneous; some specimens have strongly convex, bullate areoles in cushion-like aggregates, fixed by long stalks. Other species with minute, subglobose spores occurring in the Sonoran region are Verrucaria bernaicensis, V. bernardinensis, and V. zamenhofiana, all of them with perithecia within the areoles and lacking an involucrellum.